The immediate reaction would be to laugh about this and then move on, there is no cap space for him....but wait. I'm not sure what his cap situation would be for a team who trades for him at the deadline, but it would likely be less than $5MM. That's a doable thing if some players would be interested in redoing a contract and getting their money now instead of later.
His 11.5 cap hit for the next 2 years is reasonable for a player of his talent and impact, and I think it would be possible to fit him in next season. We also have 2 second round picks in the next draft, as well as multiple picks in the later rounds. IIRC at one point I remember reading were the Pats were likely to have 11 draft picks when the comp picks are added.
For a team looking to rebuild with a very young QB, a 2nd and 5th would be a nice haul for a guy like Peterson, and that would be something the Pats could well afford.
I think Rowe's groin issues look like they might linger this year and thus make him someone they can't rely on, and thus make adding secondary help more of a priority than we'd like.
Though I think us trading for Peterson is unlikely in reality, it's more than logical for those who like to speculate.